1. Field of the Invention
The invention relates to a tensioning means for traction mechanisms, especially a belt tensioning means, having a receiving and mounting housing, a pulley carrier pivotally connected to the receiving and mounting housing, a bearing which supports the pulley carrier relative to the receiving and mounting housing, and a spring located between the pulley carrier and the receiving and mounting housing for applying the tensioning force.
One special tensioning means for traction mechanisms is addressed in particular, that is, a belt tensioning means. The tensioning means for the traction mechanisms to which the invention relates is always addressed and described as a belt tensioning means. However, the described belt tensioning means can also be used for traction means in different ways, not only as a belt tensioning means.
2. Description of Related Art
In motor vehicles, various secondary assemblies are driven by the vehicle engine, for example, a generator, a water pump for water-cooled vehicle engines, a servo pump for motor vehicles with power steering, and a compressor for the air conditioner. Driving the secondary assemblies takes place via a main pulley on the crankshaft of the engine and a continuous drive belt which runs around the main pulley and around auxiliary pulleys on the drive shafts of the secondary assemblies. The adjustment and preservation of a predetermined tension of the drive belt are of special importance for the serviceability of the secondary assemblies and for the service life of the drive belt. To improve the serviceability of the secondary assemblies and to increase the service life of the drive belt, in general, a spring-loaded belt tensioning means is used which generally has a damping means, so that slip and vibrations can be equalized or reduced.
Recently, so-called belt starter generators (RSG which are also called integrated starter generators (ISG)) have been used in the train of pulleys. For the belt starter generators, the current flows through the generator and the generator is used as an electric drive. The main pulley, and thus the crankshaft of the vehicle engine, are accelerated roughly to idle rpm via the drive belt, whereupon the motor vehicle engine is then started. The starting phase in which the generator is used as an electric drive generally last less than one second.
The basic structure of a belt tensioning means—the receiving and mounting housing, the pulley carrier which is pivotally connected to the receiving and mounting housing, the bearing which in general radially and axially supports the pulley carrier relative to the receiving and mounting housing, a spring between the pulley carrier and the receiving and mounting housing for applying a tensioning force, and optionally a damping means—is known in many versions, for which reference is made to German patent publication nos. DE 41 34 354, DE 433 36 467, DE 43 00 178, DE 44 287 683, DE 196 03 558 and European patent publication EP 0 858 563. There are important differences principally with regard to the damping means employed in most belt tensioning means.
Published German Patent Application DE 42 43 331 discloses a contact transmission in which a drive wheel drives two driven wheels of two camshafts via a toothed belt, and as is generally conventional in the art, a belt tensioner is located on the slack side to produce the necessary belt tension. To reduce the tension peaks acting on the toothed belt in the area of the resonance points, in this contact transmission on the driving side—which is also often called the load side—there is another, elastically supported tension roller. This second tension roller is designed to prevent rapid fatigue of the toothed belt, by the variable tension components on the toothed belt, in the two directions by being cushioned and damped to a limited degree.
If the conventional belt tensioning means which is between the motor vehicle engine and the generator in normal operation on the slack side is used in conjunction with a belt starter generator, the use of the generator as an electric drive leads to the slack side becoming the load side or the driving side. This leads to the belt tensioning means being deflected against the tensioning force which has been applied by the springs. This in turn leads to less tension on the drive belt, and thus, to a degraded drive of the motor vehicle engine by the generator, operated as an electric drive, as a result of the slip. In order to compensate for this reduced tension of the drive belt which occurs in the starting phase, the belt tension would have to be increased overall, then the higher tension of the drive belt which is actually undesirable in “normal” generator operation would lead to premature wear of the drive belt, belt pulleys and secondary assemblies.